Re: [net-next 3/3] ip_gre: cache the device mtu hard_header_len calc

[Xin Long]

On Tue, Oct 10, 2017 at 4:47 AM, William Tu  wrote:
> The patch introduces ip_tunnel->ether_mtu fields to cache the value of
> dev->mtu + dev->hard_header_len.  This avoids the arithmetic operation
> on every packet.
>
> Signed-off-by: William Tu 
> Cc: David Laight 
> ---
>  include/net/ip_tunnels.h | 1 +
>  net/ipv4/ip_gre.c| 8 
>  net/ipv4/ip_tunnel.c | 3 +++
>  3 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h
> index b41a1e057fce..19565be26e13 100644
> --- a/include/net/ip_tunnels.h
> +++ b/include/net/ip_tunnels.h
> @@ -117,6 +117,7 @@ struct ip_tunnel {
>
> /* This field used only by ERSPAN */
> u32 index;  /* ERSPAN type II index */
> +   unsigned intether_mtu;  /* The mtu including the ether hdr */
>
> struct dst_cache dst_cache;
ip_tunnel is a very common structure for various tunnels.
Adding ether_mtu into it to avoid  ONLY an addition operation ONLY for
erspan, I think it's not worth it.

>
> diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
> index 6e6e4c4811cc..994b8ddea0b1 100644
> --- a/net/ipv4/ip_gre.c
> +++ b/net/ipv4/ip_gre.c
> @@ -578,8 +578,8 @@ static void erspan_fb_xmit(struct sk_buff *skb, struct 
> net_device *dev,
> if (gre_handle_offloads(skb, false))
> goto err_free_rt;
>
> -   if (skb->len > dev->mtu + dev->hard_header_len) {
> -   pskb_trim(skb, dev->mtu + dev->hard_header_len);
> +   if (skb->len > tunnel->ether_mtu) {
> +   pskb_trim(skb, tunnel->ether_mtu);
> truncate = true;
> }
>
> @@ -730,8 +730,8 @@ static netdev_tx_t erspan_xmit(struct sk_buff *skb,
> if (skb_cow_head(skb, dev->needed_headroom))
> goto free_skb;
>
> -   if (skb->len > dev->mtu + dev->hard_header_len) {
> -   pskb_trim(skb, dev->mtu + dev->hard_header_len);
> +   if (skb->len > tunnel->ether_mtu) {
> +   pskb_trim(skb, tunnel->ether_mtu);
> truncate = true;
> }
>
> diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
> index fe6fee728ce4..859af5b86802 100644
> --- a/net/ipv4/ip_tunnel.c
> +++ b/net/ipv4/ip_tunnel.c
> @@ -348,6 +348,7 @@ static int ip_tunnel_bind_dev(struct net_device *dev)
>
> dev->needed_headroom = t_hlen + hlen;
> mtu -= (dev->hard_header_len + t_hlen);
> +   tunnel->ether_mtu = mtu + dev->hard_header_len;
>
> if (mtu < 68)
> mtu = 68;
> @@ -952,6 +953,7 @@ int __ip_tunnel_change_mtu(struct net_device *dev, int 
> new_mtu, bool strict)
> }
>
> dev->mtu = new_mtu;
> +   tunnel->ether_mtu = new_mtu + dev->hard_header_len;
> return 0;
>  }
>  EXPORT_SYMBOL_GPL(__ip_tunnel_change_mtu);
> @@ -1183,6 +1185,7 @@ int ip_tunnel_init(struct net_device *dev)
>
> tunnel->dev = dev;
> tunnel->net = dev_net(dev);
> +   tunnel->ether_mtu = dev->mtu + dev->hard_header_len;
> strcpy(tunnel->parms.name, dev->name);
> iph->version= 4;
> iph->ihl= 5;
> --
> 2.7.4
>

[net-next 3/3] ip_gre: cache the device mtu hard_header_len calc

[William Tu]

The patch introduces ip_tunnel->ether_mtu fields to cache the value of
dev->mtu + dev->hard_header_len.  This avoids the arithmetic operation
on every packet.

Signed-off-by: William Tu 
Cc: David Laight 
---
 include/net/ip_tunnels.h | 1 +
 net/ipv4/ip_gre.c| 8 
 net/ipv4/ip_tunnel.c | 3 +++
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h
index b41a1e057fce..19565be26e13 100644
--- a/include/net/ip_tunnels.h
+++ b/include/net/ip_tunnels.h
@@ -117,6 +117,7 @@ struct ip_tunnel {
 
/* This field used only by ERSPAN */
u32 index;  /* ERSPAN type II index */
+   unsigned intether_mtu;  /* The mtu including the ether hdr */
 
struct dst_cache dst_cache;
 
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 6e6e4c4811cc..994b8ddea0b1 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -578,8 +578,8 @@ static void erspan_fb_xmit(struct sk_buff *skb, struct 
net_device *dev,
if (gre_handle_offloads(skb, false))
goto err_free_rt;
 
-   if (skb->len > dev->mtu + dev->hard_header_len) {
-   pskb_trim(skb, dev->mtu + dev->hard_header_len);
+   if (skb->len > tunnel->ether_mtu) {
+   pskb_trim(skb, tunnel->ether_mtu);
truncate = true;
}
 
@@ -730,8 +730,8 @@ static netdev_tx_t erspan_xmit(struct sk_buff *skb,
if (skb_cow_head(skb, dev->needed_headroom))
goto free_skb;
 
-   if (skb->len > dev->mtu + dev->hard_header_len) {
-   pskb_trim(skb, dev->mtu + dev->hard_header_len);
+   if (skb->len > tunnel->ether_mtu) {
+   pskb_trim(skb, tunnel->ether_mtu);
truncate = true;
}
 
diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index fe6fee728ce4..859af5b86802 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -348,6 +348,7 @@ static int ip_tunnel_bind_dev(struct net_device *dev)
 
dev->needed_headroom = t_hlen + hlen;
mtu -= (dev->hard_header_len + t_hlen);
+   tunnel->ether_mtu = mtu + dev->hard_header_len;
 
if (mtu < 68)
mtu = 68;
@@ -952,6 +953,7 @@ int __ip_tunnel_change_mtu(struct net_device *dev, int 
new_mtu, bool strict)
}
 
dev->mtu = new_mtu;
+   tunnel->ether_mtu = new_mtu + dev->hard_header_len;
return 0;
 }
 EXPORT_SYMBOL_GPL(__ip_tunnel_change_mtu);
@@ -1183,6 +1185,7 @@ int ip_tunnel_init(struct net_device *dev)
 
tunnel->dev = dev;
tunnel->net = dev_net(dev);
+   tunnel->ether_mtu = dev->mtu + dev->hard_header_len;
strcpy(tunnel->parms.name, dev->name);
iph->version= 4;
iph->ihl= 5;
-- 
2.7.4